Heavy-to-light hole intersubband absorption in the valence band of GaAs/AlAs heterostructures
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Heavy-to-light hole intersubband absorption in the valence band of GaAs/AlAs heterostructures M. I. Hossain,1,4 Z. Ikonic,2 J. Watson,3,4 J. Shao,4 P. Harrison,2 M. J. Manfra,1,3,4,5 and O. Malis3 1
School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA 2 Institute of Microwaves and Photonics, School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK 3 Department of Physics, Purdue University, West Lafayette, Indiana 47907, USA 4 Birck Nanotechnology Center, West Lafayette, Indiana 47907, USA 5 School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907, USA ABSTRACT We performed a thorough investigation of mid-infrared heavy-to-light hole intersubband absorption in the valence band of p-doped GaAs quantum wells with AlAs barriers. For the ptype doping a high-purity solid carbon source was used. The experimental results are compared with theoretical simulations. The inclusion of layer inter-diffusion well reproduces the transition energies. We estimate a 6-10 Å inter-diffusion length that is consistent with electron microscopy measurements. A careful analysis of our results provides valuable information for further design of emitters and detectors based on hole intersubband transitions in the valence band. INTRODUCTION Intersubband transitions within the conduction band of semiconductor quantum wells (QWs) have been widely explored, which eventually led to their application in QW infrared photodetectors (QWIPs) and quantum cascade lasers (QCLs) [1]. Since its invention in 1994 extensive research have been carried out in the field of QCLs. Different types of electron QCLs have been demonstrated including single-mode [2], dual-wavelength [3] and broad-band [4] QCLs. In stark contrast, considerably fewer experimental studies have explored in detail the properties of hole intra-band transitions. The hole intersubband transitions are particularly interesting because of their optical activity for both in-plane and out of plane light polarization, opening up the possibility of light emission or absorption perpendicular to the surface. Hole intersubband transitions between different kinds of hole states, such as between heavy and light (H-L) hole states are not subject to the same selection rules as electron intersubband transitions (polarization of light emitted and absorbed restricted to the growth direction), therefore allowing light emission and absorption in the direction normal to the semiconductor surface. This holds promise for new optical processes with applications in novel optoelectronic devices and may eventually lead to vertical cavity surface emitting lasers (VCSELs). Until now a lot of research on hole intersubband transitions has focused on Si/SiGe material system [5-8]. This is mainly due to lack of an efficient emitter to be integrated with standard Si technology. Even though intersubband absorption, electroluminescence [9-11], photocurrent measurements and QWIPs [12] have been reported in this material syste
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